The present invention relates to a digital information system, a digital audio signal processor and a signal converter, such as a digital information system for realizing the sale or supply of specified audio data or the like by transmitting it to a specified person in the form of an electrical signal, an audio signal processor and a signal converter suitable for the system, and a technique applicable for use in a data compressing and expanding circuit.
As a conventional example of commercialized information, there is a newspaper or magazine in which characters or the like are printed on paper as a medium. The paper used in this way may be replaced by various types of software stored on a memory medium, such as a floppy disk or an IC card. Another example is a communication network, such as cable television or satellite broadcasting, for supplying news or broadcast programs to specified subscribers.
Further, a portable computer, which differs from the conventional notebook-type personal computer or "electronic notebook", but which can easily send a message to another person, access a data base, or process information without being restricted by time or place, has been suggested in "Nikkei Electronics", Nov. 26, 1990, pp.116 to 124. This system proposes data transmission to a portable terminal through a public telephone or FM broadcasting or by the sale of IC cards at bookstores or station booths.
Also, a system for transmitting and receiving information is disclosed in JP-A-63-61391.
Furthermore, JP-A-61-236222 suggests a digital-to-analog converter that can be realized by a digital circuit.
In the case where information is commercialized and sold as an item which uses paper as a such as newspapers or magazines, the printing and transportation take a long time, which not only makes the system unsuitable for timely sale of information, but also adversely affects the earth's environment by deforestation to provide the materials for making paper and by the dispensing of garbage in the disposing of the paper. In the case where a IC card or floppy disk is used as a medium, such as for an electronic notebook or the like, a terminal device, such as the electronic notebook or personal computer, is needed. In addition, these terminal devices presuppose a capability for information processing, such as in the electronic notebook, so that the operation thereof is comparatively complicated and difficult in application, thereby preventing general extension of the use thereof. Also, in the case where a great amount of data are distributed through FM broadcasting, it is troublesome to select desired information, and this is also true of the satellite or cable television broadcasting, where even unnecessary information is received under a blanket contract.